On 11/18/2014 09:37 AM, Zhang Haoyu wrote: >> On Mon, Nov 17, 2014 at 01:58:20PM +0200, Michael S. Tsirkin wrote: >>> On Mon, Nov 17, 2014 at 01:22:07PM +0200, Gleb Natapov wrote: >>>> On Mon, Nov 17, 2014 at 12:38:16PM +0200, Michael S. Tsirkin wrote: >>>>> On Mon, Nov 17, 2014 at 09:44:23AM +0200, Gleb Natapov wrote: >>>>>> On Sun, Nov 16, 2014 at 08:56:04PM +0200, Michael S. Tsirkin wrote: >>>>>>> On Sun, Nov 16, 2014 at 06:18:18PM +0200, Gleb Natapov wrote: >>>>>>>> Hi Michael, >>>>>>>> >>>>>>>> I am playing with vhost multiqueue capability and have a question about >>>>>>>> vhost multiqueue and RSS (receive side steering). My setup has Mellanox >>>>>>>> ConnectX-3 NIC which supports multiqueue and RSS. Network related >>>>>>>> parameters for qemu are: >>>>>>>> >>>>>>>> -netdev tap,id=hn0,script=qemu-ifup.sh,vhost=on,queues=4 >>>>>>>> -device virtio-net-pci,netdev=hn0,id=nic1,mq=on,vectors=10 >>>>>>>> >>>>>>>> In a guest I ran "ethtool -L eth0 combined 4" to enable multiqueue. >>>>>>>> >>>>>>>> I am running one tcp stream into the guest using iperf. Since there is >>>>>>>> only one tcp stream I expect it to be handled by one queue only but >>>>>>>> this seams to be not the case. ethtool -S on a host shows that the >>>>>>>> stream is handled by one queue in the NIC, just like I would expect, >>>>>>>> but in a guest all 4 virtio-input interrupt are incremented. Am I >>>>>>>> missing any configuration? >>>>>>> I don't see anything obviously wrong with what you describe. >>>>>>> Maybe, somehow, same irqfd got bound to multiple MSI vectors? >>>>>> It does not look like this is what is happening judging by the way >>>>>> interrupts are distributed between queues. They are not distributed >>>>>> uniformly and often I see one queue gets most interrupt and others get >>>>>> much less and then it changes. >>>>> Weird. It would happen if you transmitted from multiple CPUs. >>>>> You did pin iperf to a single CPU within guest, did you not? >>>>> >>>> No, I didn't because I didn't expect it to matter for input interrupts. >>>> When I run iperf on a host rx queue that receives all packets depends >>>> only on a connection itself, not on a cpu iperf is running on (I tested >>>> that). >>> This really depends on the type of networking card you have >>> on the host, and how it's configured. >>> >>> I think you will get something more closely resembling this >>> behaviour if you enable RFS in host. >>> >>>> When I pin iperf in a guest I do indeed see that all interrupts >>>> are arriving to the same irq vector. Is a number after virtio-input >>>> in /proc/interrupt any indication of a queue a packet arrived to (on >>>> a host I can use ethtool -S to check what queue receives packets, but >>>> unfortunately this does not work for virtio nic in a guest)? >>> I think it is. >>> >>>> Because if >>>> it is the way RSS works in virtio is not how it works on a host and not >>>> what I would expect after reading about RSS. The queue a packets arrives >>>> to should be calculated by hashing fields from a packet header only. >>> Yes, what virtio has is not RSS - it's an accelerated RFS really. >>> >> OK, if what virtio has is RFS and not RSS my test results make sense. >> Thanks! > I think the RSS emulation for virtio-mq NIC is implemented in tun_select_queue(), > am I missing something? > > Thanks, > Zhang Haoyu > Yes, if RSS is the short for Receive Side Steering which is a generic technology. But RSS is usually short for Receive Side Scaling which was commonly technology used by Windows, it was implemented through a indirection table in the card which is obviously not supported in tun currently. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
